1. Field of the Invention
The present invention relates to an inorganic electroluminescent device and a method of fabricating the same.
2. Description of the Background Art
Conventionally, inorganic electroluminescent devices (hereinafter abbreviated to inorganic EL devices) have drawn attention as flat light emitting type devices. In an inorganic EL device, a high electric field is applied to a light emitting layer made of an inorganic material so as to cause electrons to accelerate. in this electric field and collide with a luminescent center, so that the luminescent center is excited to emit light.
In particular, inorganic EL devices having a light emitting layer principally composed of an alkaline earth sulfide and doped with Eu(europium) provide red light emission with high color purity. Therefore they have conventionally been regarded as components of great prospects.
JP 64-27194 A, for example, describes an inorganic EL device employing a mixed crystal of CaS(calcium sulfide) and MgS(magnesium sulfide) as a material of a light emitting layer. In the inorganic EL device, a transparent electrode, a first insulator layer composed of Ta2O5, a light emitting layer composed of Mg0.4Ca0.6S:Eu, a second insulator layer composed of Al2O3, and an upper electrode are formed on a glass substrate in this order.
The aforementioned publication describes that the inorganic EL device disclosed therein can provide improved luminance and efficiency while maintaining high color purity, through the use of the mixed crystal of CaS and MgS as a material of the light emitting layer.
In the conventional inorganic EL device, however, further improving crystallinity and optical characteristics of the light emitting layer requires MgCaS to be formed at increased temperatures. However, increasing the temperature actually degrades crystallinity and therefore deteriorates optical characteristics. For this reason, an inorganic EL device having sufficiently good luminous characteristics has not been realized.